BHP at the wheels..

[samtheman]

had my S4 2.7 dyno'd today at quattro sports, (very nice i must say!) it read 271.6 bhp engine power, but the power at the wheels was only 127 bhp.. is that normal? i've heard that with 4wd i should expect a 20-30% loss, but mine is morelike 55%!! anyone else got any dyno read outs they can post?

[DAVIDP20V]

that cant be right ?? can it ?
my girlfriends "Vauxhall" nova gsi has 110 @ the wheels ?

[img]images/graemlins/spineyes.gif[/img] [img]images/graemlins/spineyes.gif[/img] [img]images/graemlins/spineyes.gif[/img]

[samtheman]

thats what i thought.. kim at qst said it was ok, but i'm not convinced, lets wait and see what others say about it.. [img]images/graemlins/033102talk_1_prv.gif[/img]

[Paulm]

mine was 360bhp fly with 279bhp atw, I know it aint and Audi (Evo5) but 4x4 all the same.

Paul

[samtheman]

so thats 25% drop, cheers paul [img]images/graemlins/thumbs.gif[/img]

[toasty]

Pretty sure a standard S4 should read approx 200bhp at the wheels.

Sure someone here had a dyno plot to that effect.

[Ryan_s3]

something not quite right there mate,what dyno was it?dynapack?regards Ryan

[JonnyX]

I don't think you should get too hung up on percentage
power loss. The driveline transmission loss will be an
absolute figure which depends on many things (rolling
resistance, mechanical intertia, friction etc.). This is
normally approximated in a coast down run on a dyno.

Basically, a car that can get to 60 in less than 6 seconds
isn't slow. If I was you I would be more interested in the
generated power than losses etc.

[Nige_RS4]

If I was you I would be more interested in the
generated power than losses etc.

All the more reason to be interested in the wheel hp, as the conversion to flywheel hp is a mathmatical calculation based on this (unless Kim has an engine dyno) - something's amiss and I would go back and get them to do it again.

[samtheman]

i'll give kim a call on monday and see what he says. thanks for the feed back [img]images/graemlins/thumbs.gif[/img] i'll post back when its sorted

[samtheman]

something not quite right there mate,what dyno was it?dynapack?regards Ryan

i dont know, its a maha rolling road, thats all i know..

[Dippy]

...(unless Kim has an engine dyno)...

I think SFourMan might have noticed his engine being removed!

IIRC typical losses are 25-30%, and indeed flywheel power is calculated from wheel power. The fact that the flywheel power was OK suggests that some serious 'fudge' factors were being used!

[samtheman]

I think SFourMan might have noticed his engine being removed!

i wondered why it wouldn't start..[img]images/graemlins/grin.gif[/img]

[Ryan_s3]

actually a rr measures torque at the wheels from this power at the wheels is measured by a equation 5252 or something(thats why torque and bhp plots always cross there) then when they finish the power run and let the car run down by it's own speed they measure the tranmisssion loss(estimated) usually 25% ish for 4wd cars and they add this on to get estimated flywheel hp.regards Ryan

[KayGee]

My S4 is going on G-Force dyno tomorrow, hopefully it won't say 127Bhp....then again later in the week after the Miltek is fitted, and again after the upsolute....should be interesting.
Rgds
Kevin